1. Field of the Invention
The present invention relates to an ozone generator controlling apparatus for controlling an ozone generator adapted to generate ozone by applying the output of an AC power supply circuit to a single or a plurality of discharge elements connected in parallel.
2. Description of the Related Art
Ozone generators generally generate ozone by applying a high voltage with a high frequency to a plurality of discharge elements from an AC power supply circuit. In conventional ozone generators, a fuse is connected in series to each discharge element so that when an anomaly such as a discharge breakdown (local dielectric breakdown (short circuit) which occurs in a ceramic discharge surface when excess electric power greater than maximum allowable power is applied to a particular part of the effective discharge surface of some discharge element) occurs in some discharge element, the failed discharge element is separated from the circuit by melting the fuse. An example of such an ozone generator is disclosed for example in Japanese Patent Publication No. 57-45685 (hereinafter the technique disclosed in this patent will be described simply as the conventional technique).
FIG. 4 illustrates the ozone generator AO according to the conventional technique. As shown in FIG. 4, the ozone generator AO comprises an automatic voltage regulator 51, an inverter circuit 50 including thermistors 52 to 55, a transformer 56, discharge elements connected in parallel to the output of the transformer 56, fuses 58 connected in series to the respective discharge elements 57, a power supply 59 connected to the input of the transformer 56 and also to the inverter 50 in a parallel fashion, and normally-open switches 60 disposed between the power supply 59 and the transformer 56.
The automatic voltage regulator 51 converts commercial electric power to a regulated DC voltage. The inverter 50 converts the DC output voltage of the automatic voltage regulator 51 to a high-frequency voltage (1 to 10 kHz). The transformer 56 increases the output voltage of the inverter 50 to a voltage sufficiently high to generate ozone, for example, in the range of 10 to 20 kV. The high voltage output from the transformer 56 is applied to the respective discharge elements 57. If the high voltage with the high frequency is applied to the discharge elements, uniform discharge occurs between two plates of ceramic in the discharge region of the discharge elements 57. Ozone gas is generated during the process in which oxygen gas passes through the discharge space.
In the ozone generator AO, if a discharge breakdown occurs in some discharge element 57 and an excess current flows in it, the automatic voltage regulator 51 is immediately turned off to protect the semiconductor devices such as thermistors 52-55. However this causes a possibility that the automatic voltage regulator 51 is turned off before the fuse 58 connected to the discharge element 57, in which the discharge breakdown occurred, melts. In the ozone generator AO, to avoid the above problem, the normally-open switch 60 is closed immediately after the start of the operation of turning off the automatic voltage regulator 51 thereby connecting the transformer 56 to the power supply 59 having the capability of outputting a voltage equal to the output voltage of the inverter 50 so that a high voltage is still applied to the respective discharge elements 57 thus causing the fuse connected to the discharge element 57 which encountered the discharge breakdown to melt thereby ensuring that a short circuit is prevented from occurring.
In the ozone generator AO according to the conventional technique, as described above, when the output of the automatic voltage regulator 51 is cut off, electric power equal to that supplied in the normal state is supplied from the power supply 59 without interruption thereby ensuring that the fuse 58, connected to the discharge element 58 which encountered the discharge breakdown, melts. However, even after the fuse 58 melts and the discharge element 57 which encountered the discharge breakdown is isolated from the circuit, the electric power equal to that supplied in the normal state is still supplied, and thus an overload current flows through the remaining normal discharge elements 57. In the ozone generator AO according to the conventional technique, the above-described overload current can cause the remaining normal discharge elements 57 to encounter a discharge breakdown one after another.
Furthermore, in the ozone generator AO according to the conventional technique, when a discharge breakdown occurs, the only action taken is that the fuse 58 connected to the failed discharge element 57 is cut off, and it is impossible to determine which discharge element is failed and how many discharge elements are failed. This makes it difficult to quickly take a corrective action after the failure.
Furthermore, the result of the employment of fuses 58 is that a fuse 59 is needed to be replaced whenever a discharge breakdown occurs in some discharge element 57. This brings about the disadvantage that expensive and troublesome tasks are required.
In view of the above, it is an object of the present invention to provide an apparatus for controlling an ozone generator in such a manner that when a discharge breakdown occurs in some discharge element, ozone is still generated without imposing bad influence on the remaining normal discharge elements. It is another object of the present invention to provide an apparatus for controlling an ozone generator, which does not require current cut-off means such as a fuse to be replaced whenever a discharge breakdown occurs in some discharge element.